Abstract
Conventional on/off-based control split-type appliances are widely used in classrooms and offices, in Brazil and in many other countries, due to their low cost and ease of installation. However, occupants often complain about thermal discomfort depending on their position within the conditioned space, especially in positions that are directly affected by the draft, since those equipment provide high cold air velocities as a result of their high cooling capacity relatively to their air supply area. In order to improve the indoor thermal comfort in spaces conditioned by this kind of system, a simplified empirical model for controlling both the supply airflow and the temperature set-point is proposed in this work. In view of that, the comfort conditions in an occupied classroom were experimentally evaluated according to ISO 7730 Standard, which defines the thermal satisfaction in occupied environments based on the PMV index. Specifically, the speed, temperature and relative humidity of the air and the mean radiant temperature of the room were measured at 8 positions within the air conditioned space, for the three original air flows (high, medium and low) of a 10.5-kW cooling capacity appliance and three set-point temperatures (23, 24 and 25 °C). The simplified model, correlating thermal comfort and the variables that could be directly controlled by the split-type system (airflow rate and temperature), was obtained by adjusting several curves from 72 measuring assemblies (8 measuring points, 3 set-point temperatures and 3 supply airflows). The correlation that best represents the distribution of thermal comfort throughout the conditioned environment was provided by the non-linear regression method of Levenberg-Marquardt.
Highlights
Split-type equipment has been used in a large scale in residential and commercial air conditioning, being currently the most used in these environments [1]
The PMV distribution are almost equal for the three airflows, and near to the neutral thermal comfort sensations (≈ 0), with values above and below zero, i.e., this is the best situation for all the setpoints analyzed, Figure 6
This paper presented an experimental research focused on the improvement of thermal comfort in classrooms conditioned by split-type air conditioners
Summary
Split-type equipment has been used in a large scale in residential and commercial air conditioning, being currently the most used in these environments [1]. In Brazil, approximately 4 million of "high-wall split" units were sold in 2010, with capacities below 30,000 BTU/h (10.5 kW), and the perspectives of the manufacturers are to increase sales for the few years [1]. Window-type units, which accounted for 60% of sales 10 years ago, currently represent only 15%, in contrast to the 70% of split-types [2]. The popularization of the use of split-type air conditioning equipment in various types of environments indicates the need to study in detail the impact of this equipment on the thermal comfort for occupants [3, 4, 5]. In the more recent models, it has been shown that the decrease of its size leads to increasingly lower supply air temperatures, resulting in the risk of thermal discomfort in positions directly affected by the cold blowing jet [5]
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